FIG. 26 shows a conventional rotation angle detection device. Gear 38 is attached via engaged spring 39 to a rotation axis (not shown) whose rotation angle is intended to be detected. Gear 38 is engaged with gear 41 having an outer circumferential end face provided with code plate 40 to which a plurality of magnetic poles are magnetized. Magnetic poles provided on code plate 40 move in accordance with rotation of the rotation axis to be detected. The number of the magnetic poles is counted by detection element 42 provided facing the outer circumferential end face so as to detect a rotation angle. Furthermore, as a device for detecting a rotation angle of a multiple rotation rotor such as an absolute encoder, a measurement method for detecting a rotation angle of an axis to be detected from rotation angles of a plurality of rotors having phase difference is known.
Prior art information relating to the invention of this application includes Japanese Patent Unexamined Publications No. H11-194007 and No. S63-118614.
In the thus configured rotation angle detection device, the rotation angle of the axis is detected by counting the number of a plurality of moved magnetic poles disposed on the outer circumferential end face of the code plate. Therefore, in order to improve the resolution of the detection angle, the dimension of the magnetized magnetic pole should be made to be fine. Furthermore, since rotation of the code plate and rotation of the axis are carried out via a gear, it is somewhat difficult to enhance the detection accuracy, by backlash and the like. Furthermore, since this rotation angle detection device can be employed only for detection of the relative rotation angle, it is not suitable for detecting an absolute rotation angle.
Furthermore, in the above-mentioned rotation angle detection device, due to arrangement accuracy and center deflections of gears, detection error in the rotation angle detection unit, or the like, the detection accuracy of the rotation angle of an axis to be detected may be deteriorated.